Four co-principal and two collaborating investigators will utilize core facilities and collaborate and cooperate to investigate the biology, biochemistry, and somatic cell genetics of cells involved in the immune response. Wherever possible, they will use cloned cultured cell lines and derive from them somatic cell variants with defects in specific immunological function. Special efforts will be made to chemically characterize the molecules directly involved in immunological functions. Particular attention will be paid to structural basis of the functions of H-2 antigens; the genetic and molecular mechanisms involved in the somatic generation of antibody diversity and the switching of classes; the structural basis of antibody effector functions; the molecular mechanism responsible for the immunological and phagocytic roles of macrophages; the role of NK cells in resistance to infectious agents and tumors; and the structural basis of idiotype and the role of idiotypes in auto immune disease.